The present invention relates to a method of recording information on an optical recording medium and, particularly, to a method of recording information on a write-once type optical recording medium. The invention also relates to an information recording apparatus for recording information on an optical recording medium and, particularly, to an information recording apparatus for recording information on a write-once type optical recording medium.
Recently, proposals have been made on next-generation optical media having a recording capacity much greater than that of media in the related art and allowing a very high data transfer rate to be achieved, and some of such media have already been put in practical use (see Patent Document 1). Unlike optical recording media in the related art, recording and reproduction of data in and from such a next-generation optical media is performed using a laser beam having a wavelength of about 405 nm and an objective lens having a numerical aperture of about 0.85. As a result, the diameter of a laser beam spot on a recording surface is as small as about 0.39 μm, and it is therefore possible to achieve a recording capacity of about 25 GB/side and a data transfer rate of about 36 Mbps at a reference line speed.
Proposed next-generation optical recording media are similar to existing optical recording media such as CDs (compact discs) and DVDs (digital versatile discs) in that they include various types of optical recording media such as reproduction-only types, write-once types, and rewritable types. It is known that a greater amount of heat per unit time is required to record data in write-once type media as recording line speed increases. In order to increase the amount of heat per unit time, it is necessary to use a semiconductor laser having greater power or to increase the length of an on pulse pattern, i.e., to increase the time during which the intensity of a laser beam is set at a recording power level.
Patent Document 1: JP-A-2003-203383
However, a laser beam used for next-generation optical recording media is light in the wave range of blue, and a semiconductor laser capable of emitting such a laser beam at high power is very expensive. If the laser beam is set at the recording power level for a too long time, unwanted accumulation of heat occurs in a recording layer when a long recording mark is formed, and resultant thermal interference causes the problem of degradation of recording characteristics.
One effective solution to such problems is to perform preheating by applying an assist pulse having a lower intensity when intervals between recording marks or space regions are formed. However, when the assist pulse is uniformly applied regardless of the lengths of the space regions to be formed, another problem arises in that the pulse application is too long for a recording mark preceded by a short space region and is conversely too short for a recording mark preceded by a long space region.